The center of interest in the proposed research is the structure-function relationships of certain proteins involved in iron metabolism. Of major interest is the nature of iron binding and release by siderophilin (transferrin) from human plasma and by conalbumin, an analogous protein from hens egg white. Physical chemical studies of these proteins and of their complexes with various metals and anions will make use of difference, fluorescence, EPR and Mossbauer spectroscopy, titration, and analysis of the kinetics of complex formation and dissociation. The goal of these studies is an adequate understanding of the factors which control the interaction of these proteins with iron and carbonate ions under physiological conditions. Structural and amino acid sequence studies of the active binding site regions of the proteins for iron and carbonate ions will be aimed at a greater understanding of the apparently contradictory phenomena of high stability of the iron-carbonato-protein complexes (Kassoc equals ca. 10 to the 25th power) and the ready acquisition of the bound iron by erythropoietic tissue under physiological conditions. Well-known methods of chemical and enzymic cleavage and sequence analysis of proteins will be used. Binding site identification will be sought through various techniques for labelling the peptide regions involved in binding. Elucidation of the physiological mechanism of iron acquisition from iron-carbonato-protein complexes by erythropoietic tissue is the goal of studies of the interaction of various metal-anion-protein complexes with reticulocytes. Substitution of various metal ions for iron and various anions for carbonate in the normal complex promise to yield valuable information regarding the normal physiological mechanism. Radioactive tracer techniques will be the major tool in these studies.